Current medical practice requires some body cavities, organs (e.g., the bladder or kidney), spaces (e.g., the pleural space), or wounds of patients to be drained of fluid whether in the liquid form (e.g., urine or blood) or gaseous form (e.g., air, gas) or a gas/liquid mixture (e.g., frothy exudate). For example, current medical practice includes draining blood in a hemothorax and air, gas, or frothy exudate from a pneumothorax.
Examples of urine drainage include urinary catheters inserted via the urethra, nephrostomy tubes, and suprapubic catheters. Nephrostomy tubes are inserted directly in the calyx of the kidney through the patient's back to drain urine from the kidneys. A suprapubic catheter drains urine out of the bladder but is inserted directly into the bladder through the abdominal wall, instead of through the urethra.
Examples of chest and thoracic drainage include pleural drains that are inserted in the pleural space and drain air, gas, or blood or a mixture of both from the pleural space via a chest tube and a chest drainage system, such as the Pleur-evac.
Examples of blood drainage include chest tubes for evacuating blood from a hemothorax, wound drainage catheters, and surgical drainage collectors.
An example of mediastinal drainage includes a pericardial catheter that drains blood from the pericardium, the sac surrounding the heart.
Examples of gastrointestinal drainage include nasogastric catheters and drainage tubing that empties into a collection vessel.
It is also widely accepted that to control infection, fluid that has drained from a patient should not be allowed to flow back to the patient.
Also, a drainage system can be active or passive. A passive system can be gravity-operated such as a urine drainage system. An example of an active drainage system is a chest drainage system where a vacuum is applied to the drainage system.
As one particular example, urinary catheters are commonly used for patients who are undergoing surgery, incapacitated due to a spinal injury or pelvic fracture, incontinent with open sacral or perineal wounds, or incapable of voluntary urination in order to permit the drainage of urine. A urinary catheter, such as a Foley catheter, is a flexible, sterile tube that is inserted into the bladder via the urethra to allow the urine to drain into a collection receptacle. Foley bags are a common drainage collection receptacle used to collect urine from a Foley catheter inserted in the urethra. Urine is transferred to the collection bag via a drainage tube connected to the catheter.
A primary risk with urinary catheters is their contribution to urinary tract infections. A urinary tract infection (UTI) is considered a “never” event for which a hospital is not reimbursed by Medicare for treatment costs and also cannot charge the expenses to patients. Therefore, there are incentives for hospitals to follow best practices in order to avoid or reduce catheter associated UTI occurrences in their patients. Accordingly, as one guideline, the Center for Disease Control (CDC) recommends, at page 13 of the 2009 Guidelines for Prevention of Catheter-Associated Urinary Tract Infections, to “keep the collecting bag below the level of the bladder at all times” (Category 1B). This guideline is to prevent backflow of urine to the bladder from the collection receptacle by gravity.
To meet this recommendation, the drainage collection bag is usually hooked onto a support (such as a rail or hospital bed) at a location below the level of the bladder. Most collection bags are also vented, so that the intraluminal pressure of the receptacle and empty drainage tubing is at atmospheric pressure, which facilitates gravity dependent drainage.
It is important for the collecting bag to be hooked below the level of a patient's bladder to help keep the flow of urine downhill towards the collection bag. However, when transporting a patient, the drainage collection bag is often placed on the patient's abdomen or on the transport gurney instead of at the proper lower hanging location. This is usually performed to avoid rips and urine spills due to the collection bag protruding from the gurney when at its proper hanging location.
A problem with placing the collection bag on the belly of the patient is that when the bag is higher than the bladder, it is possible for urine in the bag or tubing to flow back to the patient. This backflow of urine can cause infection and patient discomfort.
Although backflow is a recognized problem, on any drain bag or urine meter bag available on the market, if the bag is squeezed, held upside-down, or held above the level of the patient's bladder, it will not stop 100% of urine from going backwards. Unfortunately, one way-valves (non-return or non-reflux valves) cannot be used to prevent back-flow of urine because the CDC Guidelines for Prevention of Catheter-Associated Urinary Tract Infections (1981 and 2009) state that an unobstructed flow of urine should be maintained.
The unobstructed flow of urine is important because when patients are catheterized, many are passing blood and clots in their urine. In some cases, stones and sediment are passed by the patient. Further, there is often viscous low output urine. If an anti-reflux mechanism or valve is in place, the danger is greater of impeding the free flow of urine and creating a clogging effect at the anti-reflux mechanism. The clogging effect may cause a standing column of urine that may back right up into the patient.
Recent anti-reflux chambers are designed to be an elevated dome chamber above the bag with a right angle then leading into the drainage tubing, which minimizes urine from going back to the patient through the drainage tubing. However, in certain orientations such as the reflux chamber being on the dependent side, the anti-reflux chamber fails and urine is still able to flow retrograde through the anti-reflux chamber and re-enter the drainage tubing.
Another problem with current urinary catheter and drainage bag systems is that when the collection bag is hooked onto the support, the drainage tube between the catheter and the collection bag contains excess slack. As shown in FIG. 1A, this excess slack in the drainage tube 13 between the catheter 14 and the collection bag 10 hooked onto the support 12 (via hook 11) creates a loop (see encircled section), that serves as a basin into which fluid will pool. The term loop in this application will mean any loop, U-loop, and inflection point in a drainage assembly where liquid can accumulate and/or obstruct a cross-section of the tubing.
When the fluid level within the loop rises to fill the tubing's cross-sectional area (see line at trough of FIG. 1B), two separate airspaces are formed (airspace U and D) and air pressure between the two airspaces can no longer equilibrate across the fluid-filled Loop. The air pocket upstream of the loop (airspace U of FIG. 1B) is effectively trapped because it cannot escape back toward the patient or downstream to the drainage bag 10. As more urine flows out, the upstream meniscus U rises and compresses airspace U. Because the trapped amount of air in airspace U is being squeezed into a smaller volume by the rising meniscus U, the pressure in airspace U rises and resists the rise of meniscus U. Thus, as more urine collects in the urine-filled loop, meniscus U barely moves up while meniscus D, which is exposed to atmospheric pressure via the vented collection bag, rises. The rise in pressure in airspace U generates a backpressure that is transmitted back to the bladder 20.
Because the bladder is highly compliant, the bladder responds to backpressure by stretching and accommodating greater undrained urine volumes, while maintaining low intravesical (bladder) pressure. Fluid will accumulate within the bladder until intravesical pressure exceeds the back-pressure caused by the air-lock obstruction of airspace U. The pressure at airspace U equals the difference in elevation H between menisci U and D. The maximum difference in menisci elevation across the loop effectively sets the pressure and bladder volume thresholds before urine can crest over the downstream (distal) apex and flow into the collection bag. In-vitro tests have shown that back-pressures of 20 cm H2O can exist due to a urine-filled loop. The relationship between bladder pressure and volume of urine in the bladder can be understood by reference to the cystometrogram of FIG. 2. As can be seen by the basal cystometrogram, a 20 cm H2O backpressure on the bladder means that about 425 ml of urine is trapped in the bladder. This high volume of undrained urine is likely a risk factor for urinary tract infections.
Accordingly, there continues to be a need in the art for improved devices and procedures for minimizing the instances of infections and/or reduce backflow or backpressure contribution to those instances of infections.
Although this background describes certain specific applications and problems, embodiments of the invention should not be construed as limited to or requiring the solving of all of these problems.